1. Field of the Invention
The present invention is intended for use in the unloading of bulk bags used as containers for particulate materials. The present invention is particularly intended for use in unloading bulk bag containers filled with dry or moist materials. The present invention is most particularly intended for use with bulk bag containers fabricated from cloth like material, such as woven polyester material, which is usually sewn in a cubicle configuration.
2. Description of the Prior Art
Bulk bags made of heavy cloth material have been known in the prior art for some time. It has also been known to provide one surface of the bag with heavy corner straps which will support the bag when it is hung in a tower like supporting frame. It has also been known to provide an opposite surface of the bag with a central cylindrical outlet which is closed by draw and tie strings.
Typically, the bulk bags may hold about 2,000-2,500 pounds; however, it is not uncommon to have bulk bags which are much heavier or much lighter. One standard bulk bag, commonly called a one ton bag, is about 64 cubic feet in volume.
The bag is generally sized to fit on a standard pallet and the actual weight of the bag will depend on the density of the contained material. When the bag is hung in the support frame and emptied, the sides begin to move in and straighten out during discharge of the material. At some point during the discharge, the side walls begin to collapse and the bag will elongate to a conical configuration. While this is a preferred result, the desired elongation does not always happen naturally. The failure to elongate into the desired cone configuration is particularly troublesome when the bulk material is a powder or other non-free flowing material. The failure to flow into the desired cone configuration typically results in inefficiency and often prevents total discharge of the bulk materials.
One additional factor which contributes to the difficulty of unloading a bulk bag is the material's angle of repose. As the angle approaches 90.degree., the material becomes more difficult to unload since it tends to stack rather than flow to the opening. By way of comparison water may be thought of as having a zero angle of response. Thus, water flows freely and tends to seek its own level.
Despite the fact that bag elongation has been a desirable characteristic of the unloading process, the prior art has not generally addressed this element of the process. In the past there have been efforts to accomplish bag elongation by raising the bulk bag via the lifting straps while maintaining the bag outlet in a fixed position. While this effort recognized the desirability of elongating the bag, it has proven to be less cost effective than desired and requires substantial modifications of the supporting frame within which the bag is hung.
Despite the above effort at bag elongation, most bulk bag unloading systems do not include such an elongation system. In one common system, the cylindrical outlet or discharge spout of the bulk bag is placed in a very shallow walled hopper and the entire hopper and bag are vibrated or gyrated. In another system, the cylindrical outlet spout of the bulk bag is placed on a rocker mechanism which also supports the bag. Both of these prior art attempts seek to discharge all of the material, however, neither approach allows the bag to elongate. None of the prior art approaches fully addresses the problems associated with the angle of repose. As a result, the prior art creates poor flow characteristics and problems with pockets of residual material within the bags. As one alternative to the prior art, the bulk bag can be held over a totally open receiving vessel and the materials discharged without any effort to control the flow through an outlet spout. While this latter course may be acceptable with some materials, it is not considered a generally workable solution to the problem. The rapid discharge of material without control over the flow can create severe area dusting and atmospheric contamination problems which are environmentally unacceptable and/or create problematic ambient air conditions in the workplace.
In view of the above, it was concluded that the art desired a practical, efficient means for elongating a bulk bag container at an unloading station while maintaining control over the dispensed material.